The exemplary embodiments described herein relate generally to semiconductor devices and methods for the fabrication thereof and, more specifically, to methods for reducing adhesive debonding forces between semiconductor layers and substrates in post-bonding processes.
Optoelectronic devices such as solar cells may incorporate flexible semiconductor layers produced by spalling techniques. In these spalling techniques, a stressor layer is generally used to exfoliate a thin, device-quality, semiconductor layer from a parent semiconductor substrate. This process can be repeated multiple times, limited only by the thickness of the substrate. The thin semiconductor layers (which may be flexible) can be difficult to handle and process.
In some cases, spalling may involve the temporary bonding of a flexible semiconductor layer to a (preferably rigid) low-cost handle substrate and subsequent separation of the flexible semiconductor layer from the handle substrate using ultraviolet (UV) releasable tape or polyimide releasable tape. In such spalling techniques, the bonding method should be compatible with semiconductor layer/handle substrate processing at temperatures as high as 200 to 400 degrees C. The bonding temperature is limited by the maximum temperature which can be handled by the tape (maximum temperature of about 90 degrees C. for UV tape and about 200 degrees C. for polyimide tape) contacting the stressor layer used for spalling.
Bonding using an epoxy adhesive is one type of bonding method. However, post-bonding processes at temperatures higher than the curing temperature of the epoxy may lead to both blister formation and adhesion failure between the impermeable flexible film and the epoxy, an effect attributed to epoxy outgassing.